Cryogenically frozen plain steel and phosphor bronze wound, loop end. Their Medium gauge, 011 016 026w 040w (2 each). Sealed in corrosion-free "NitroPack" packaging. Maker says: "With feedback from players young and old, we have developed a series of strings gauged for the current needs of the musician, and then cryogenically treated them to ensure that if you're playing into the night, these sets will continue to inspire and help you share your unique voice." GHS A275 Americana Cryogenic Phosphor Bronze Medium Gauge Mandolin Strings